The present invention relates to a milling or cutting engine for excavating trenches in the ground, and more particularly such an engine of the type having at least one substantially vertical support plate on each side of which two cutting milling drums are mounted for rotation about an axis substantially perpendicular to the plate.
Machines of this type are already known, which generally have two support plates, holding four milling drums turning inversely in pairs so as to bring the excavated dirt toward an aspirating nozzle situated at the axis of the machine.
As the capacity of such milling engines is increased, it becomes necessary to increase the thickness of the plate, which has to withstand the stresses placed on the milling drums by the ground.
This thickness of the plate creates difficulties in cutting the trench. The cutting tools mounted on the two milling drums beside the plate must be sufficiently apart from one another to accommodate the advance of the plate as the milling drums revolve. The result is the formation of a soil web on the bottom of the trench, the web having a width generally equal at least to that of the plate.
When the milling engine is lowered, the bottom edge of the plate abuts against this web and can therefore stop the progress of the cut.
A variety of solutions to this problem have been proposed. Consideration has been given to mounting the cutting tools situated beside the plate so as to move on the milling drums, so as to bring these tools on the two milling drums against one another when they are in a position clear of the plate. This solution, however, has proven difficult to realize inasmuch as the axes of the articulation of these tools must be able to withstand extremely great stresses.
Circular grooves have also ben created in the plate, centered about the axis of the milling drums, so that the cutting tools mounted fixedly on the milling drums will be separated by a distance less than the thickness of the plate. This solution has proven somewhat satisfactory, however, with the plate thicknesses presently used, it still is true that the web remains sufficiently large to withstand the weight of the milling engine applied through the bottom surface of the edge of the plate.